The insert molding by an injection molding method has been widely used in the prior art, in which an insert component is covered with resinous material in conformity with the contour of the former.
Generally, in the injection molding method, an insert component is located and fixed at a predetermined position within a cavity of a mold made, for example, of metal and is clamped in this state. Then, molten resin injected from a nozzle of a molding machine is filled in the cavity via a sprue, a runner and a gate to cover the outer circumference of the insert component in conformity with the cavity-forming surface, thus forming the insert-mold product.
In the above-mentioned injection molding method, however, it is necessary to apply and maintain a high pressure in the interior of the mold after the molten resin has been filled in the cavity, for the purpose of ensuring the accuracy of the contour of the mold product while complementing the volume contraction of the molten resin accompanied with the solidification thereof.
Accordingly, as the mold must have a high mechanical strength durable against such a high pressure, there is a problem in that a cost of the mold is high.
Also, as the insert component disposed in the cavity is exposed to the high pressure, there is another problem in that it is impossible to directly carry out the insert molding while using a relatively fragile component as an insert component, such as a glass pipe or a bare chip.